Weld fitting

ABSTRACT

A coupling for use in forming a welded tube joint is disclosed along with a method for forming such joint. A thin coupling sleeve is tightly swage-fitted onto the end of a tube to form a male or female tube end assembly suitable for engagement with a tubular mating part assembly which may be a fitting or another coupling sleeve and tube assembly. The male-female interlocking arrangement provides radial and axial alignment of the joined assemblies. The structure is arranged to provide a space between the tube end face and the interior end face of the tubular mating part assembly. During the welding operation, external fusion heat is applied to form a single weld bead extending from the interior of the tube to the exterior surfaces of the assemblies. The width of the weld at its inner radial extremities is longer than the axial width of the space between the interior end faces and its width at its outer radial extremities is at least equal to twice the axial length of the male-female telescoped portion so that all the members are fused into a single unitary structure.

O United States Patent [1 1 3,635,498 Patel [45] Jan. 18, 1972 [54] WELD FITTING I Primary Examiner-Dave W. Arola [72] Inventor. Hu-alal V. Patel, Cleveland, Ohio An0mey McNenny Farrington, Pea-me & Gordon [73] Assignee: The Weatherhead Company, Cleveland,

Ohio [57] ABSTRACT [22] Filed: Dec. 15, 1969 A coupling for use in forming a welded tube joint is disclosed Appl. No.: 885,018

along with a method for forming such joint. A thin coupling sleeve is tightly swage-fitted onto the end of a tube to form a male or female tube end assembly suitable for engagement with a tubular mating part assembly which may be a fitting or another coupling sleeve and tube-assembly. The male-female interlocking arrangement provides radial and axial alignment of the joined assemblies. The structure is arranged to provide a space between the tube end face and the interior end face of the tubular mating part assembly. During the welding operation, external fusion heat is applied to form a single weld bead extending from the interior of the tube to the exterior surfaces of the assemblies. The width ofthe weld at its inner radial extremities is longer than the axial width of the space between the interior end faces and its width at its outer radial extremities is at least equal to twice the axial length of the malefemale telescoped portion so that all the members are fused into a single unitary structure.

10 Claims, 4 Drawing Figures warn rrrrruc BACKGROUND OF THE INVENTION This invention relates generally to tube couplings and more particularly to a novel and improved welded tube coupling and a method for making such a coupling.

PRIOR ART Various types of welded tube couplings are known. For example, the US. Pat. Nos. 3,194,936; 3,248,134; and 3,439,941 all relate to such couplings. The Nicol US. Pat. No. 3,439,941, assigned to the assignee of thepresent-invention, illustrates acoupling arrangement which is particularly useful for use with high strength tubing such as precipitation hardened stainless steel andthe like. In the Nicolstructure, sleeves are positioned onthe ends of tubesand thesleeves are provided with interfittingmating end surfaces arranged to insure radial and axial alignment of the coupling halves prior to welding. The sleeves cooperate to support the tube ends inthe area of theconnecting .welds so that'the welded coupling provides a joint which is at least substantially as strong as the tubing itself and is capable of reliably absorbing the loads applied to the tubing system.

Although couplings as disclosed by Nicol are very satisfactory for use with tubing formed of many types of materials,.difficulties are sometimes encountered when such a couplingarrangement is utilized in conjunction with tubing formed of materials having certain physical properties such as high notch sensitivity, relatively low rates of heat conductivity, and relatively high sensitivity to contamination difficulties. When, for example, the structure as disclosed in Nicol is utilized to join tubing formed of titanium or titanium alloys, difficultycan be encountered because such tubing is extremely notch sensitive and is susceptible to damage in'the areas of any stress concentrations. Similarly, the relatively thick wall thickness required, from a practical standpoint, in the sleeves of the Nicol device in order to provide the male-female relationship illustrated therein, tends to result in weld puddle control problems because of the high energy input required for penetration of the thick section.

SUMMARY OF THE INVENTION A welded tube coupling in accordance with the present invention is particularly suitable for use with tubing formed of materials which tend to have relatively high notch sensitivity, tend to have a relatively low heat conductivity, and tend to be relatively sensitive to contamination problems.

In accordance with one embodiment of this invention, a coupling includes two coupling halves each provided with a sleeve positioned around the tube end and axially located with respect thereto so that one sleeve projects beyond the associated tube end and the other sleeve is spaced back from its associated tube end. This structure is arranged so that a malefemale arrangement is provided in which the exterior of the surface of the tube of the male coupling is proportioned to telescope into the sleeve of the female coupling half to provide radial alignment between the two coupling halves prior to welding. The ends of the sleeves abut to provide axial location between the two coupling halves.

In such embodiment, the structure is arranged so that the two tube ends are spaced a predetermined distance apart when the sleeve ends abut to facilitate purging of the coupling to eliminate contamination problems in the weld.

With this structure wherein the tube coacts with its as sociated sleeve to provide the only interfitting surfaces, the sleeve can be formed with substantially any desired thickness and can, if desired, be formed with a very thin wall section. Preferably, the relationship between the wall thickness of the sleeve and the wall thickness of the tube is selected so that the sleeves provide sufficient support for the tube ends to com pensate for the weakening of the tube end material caused by the heat of welding without providing excessive rigidity which would produce undesirable notch sensitivity problems.

Further, such relationship can be selected so that the amount .cientclearance so that they can be easily slipped over the ends of thetube and the tube is then radially expanded into tight engagement with the sleeve to frictionally lock the sleeve with respect to the associated tube. Such internal swaging is particularly desirable when the sleeve has a wall thickness less than the wall thickness of the tube andsresults in an assembly wherein the tube is subjected to compressive stress while the sleeve is subjected to .tensile stress to insure tight engagement along their interface.

In accordance with another aspect of this invention at least the portion of the sleeves spaced from theweld are provided with a lubricant film so that radial support can be provided for the tube without producing stress concentrations or wear even when the loading applied to the tubing system tends to produce relative movement between the sleeve and tube. Such a lubricating film is particularly desirable when the materials forming the couplinghave a tendency to gall and fret when relative sliding movement between surfaces occur. For example, titanium tends to present this problem and the lubricating film virtually eliminates such problem.

BRIEF DESCRIPTION OF THE DRAWINGS FIG.'1 is a longitudinal section of two pieces of tubing fitted withthe female and male coupling sleeves of this invention prior to roll swaging with one tube broken away to illustrate thelubricating coating;

' FIG. 2 is a longitudinal section similar to FIG. I after the roll-swaging process has been performed to lock the sleeves on their associated tubes;

FIG. 3 is a longitudinal composite section illustrating in its upper portion the coupling halves positioned-for welding and in its lower portion the completed welded connection; and

FIG. 4 is a composite view, partially in longitudinal section, illustrating an embodiment in which a coupling half is joined to an elbow fitting with the upper portion of this figure again illustrating the structure prior to the welding operation and the lower portion of the figure illustrating the structure after the welding operation has been performed.

DETAILED DESCRIPTION OF Til-IE DRAWINGS Referring to FIGS. 1 through 3 of the drawings in greater detail, two similar pieces of tubing 10 and 12 fitted with coupling sleeves l4 and 16 so as to form a female coupling half assembly 13 and a male coupling half assembly 115. The coupling sleeve 14 is initially formed with central bore 18 having a suitable diameter so as to slip over the tube 10 with a relatively close fit. As illustrated in FIG. l the axially extending portion 20 of the sleeve 14 is outwardly flared to an appropriate degree so that when the tube 10 is expanded by roll swaging to the assembled condition illustrated in FIG. 2, the axially extending portion 20 and the remaining portion of the sleeve 14 have a substantially cylindrical configuration. As shown in FIG. 2, the sleeve 14 has an expanded inside diameter substantially equal to the outside diameter 24 of the expanded adjacent tube 10 along the entire sleeve length. The drawings exaggerate the degree of expansion for illustration purposes and it should-be noted that the tube member is preferably expanded so as to obtain about 3 to 5 percent reduction in wall thickness when the tubing is formed of titanium or the like.

The male assembly or coupling half 15 is formed by the tube 12 and the sleeve 16. The sleeve 16 is also initially formed with a central bore 26 proportioned to slip over the tube 12 with a relatively close fit. The sleeve 16 is properly positioned around the tube 12 so as to provide a circumferential exterior recess, generally indicated at 28. The tube 12 is similarly expanded by roll swaging into the sleeve 16 so as to provide an expanded outside tube diameter 30 substantially equal to the outsidetube diameter 24 of the expanded female assembly 13 as shown in FIG. 2.

The axially extending portion 20 of the sleeve 14 has a greater axial length as measured from the end face 32 of the adjacent tube to the end surface 34 of the extending portion than the corresponding axial depth of the circumferential exterior recess 28 as measured from the end face 36 of the tube 12 to the end surface 38 of the adjacent sleeve 16. The telescoped portion of the mating assemblies has an axial length of from about 0.030 to about 0.040. However, the drawings exaggerate the dimensions for purposes of clarity. When the mating assemblies are placed in abutting engagement, the interior .tube end faces 32 and 36 are separated by a space 40, defined by the end faces 32 and 36, and the interior surface of the sleeve 14, as best shown in the upper portion of FIG. 3. The space 40 has an axial length of about 0.002 to 0.006 inches and this dimension has again been exaggerated in the drawing for purposes of clarity. This space is provided to facilitate an inert gas purge prior to the welding operation so as to prevent contamination of the weld.

When the interfitting mating surfaces of the assemblies are engaged, axial and radial alignment is assured. Radial alignment is necessary before the end of the tube 12 can move into the sleeve 14. Similarly, the tubes must be axially aligned if the two sleeve end faces 34 and 38 engage around the entire periphery. Therefore, a visual inspection can be used to determine if the two halves are properly positioned.

When the mating assemblies are properly engaged, as determined by visual or manual inspection, the joint formed by the abutting end surfaces 34 and 38 of the coupling sleeves l4 and 16 will lie in a predetermined spaced relationship with respect to the space 40 between the end faces 32 and 36 of the tube members 10 and 12. Thus, the joint also serves as a visible means to accurately locate the electrode during a fusion welding process. Accordingly, the mating assembly members may be joined by a single weld bead 42 produced by externally applying fusion heat substantially along the joint, as shown in the lower portion of FIG. 3. The weld bead extends from the inner surface of the tube members to the exterior surfaces of the assemblies. The width of the weld bead at its inner radial extremity is larger than the width of the spaces 40 previously separating the tube end faces and the tube members are also fused by the single weld. At the exterior surfaces of the assembly, the width of the weld bead 42 is at least equal to about twice the axial spacing between the space 40 and the sleeve end surface so that a single unitary structure results.

The following are examples of specific dimensions which have been used for the manufacture of a welded tube cooling for titanium tubing. The sleeves in each case were formed of the same material as the tube. For a 3/ 16-inch tubing having a wall thickness of 0.016 inches, the sleeves were provided initially having an inside diameter of about 0.193 inches and a wall thickness of about 0.07 inch. The male sleeve length was about 0.25 inch and the female sleeve length was about 0.31 inch. In another weld coupling for is-inch titanium tubing having a wall thickness of 0.036 inch, the sleeves wereprovided with an inside diameter of about 0.632 inch and a wall thickness of about 0.0]4 inch. In this instance, the male sleeve had a length of about 0.657 inch and the female sleeve had a length of about 0.717 inch. I

in each of the above examples the sleeves were positioned over the ends of the associated tubes and the tubes were internally swaged to increase their diameter 'until the thickness of the tube wall was reduced about 4 percent.

As illustrated in the above embodiment of this invention, the male-female interlocking arrangement characterized by single lip mating permitted the use of a coupling sleeve having a wall thickness substantially less than that of the adjacent tube and approaching about one-third the thickness thereof. Consequently, the total wall thickness was not greatly increased and stress concentration problems were not particularly significant. A coupling in accordance with this invention provides support in the heat weakened weld zone with a minimum increase in the stress concentration problems. In addition, the reduction in total wall thickness at the weld location, as compared to coupling arrangements formerly known in the art, alleviates the weld puddle problem since less heat is required to penetrate the total wall.

Another embodiment of this invention is illustrated in FIG. 4, which shows an expanded tube identical in structure to the tube 12 and a sleeve identical to the sleeve 16, as shown in FIGS. 2 and 3. However, in this embodiment, the coupling connects the tube to an elbow fitting 44. Of course, other types of fittings can be provided and the elbow 44 is illustrated only by way of example. The elbow 44 has a central bore 46 having a diameter equal to the inner diameter of the tube 12. As shown in FIG. 4, the elbow provides a female mating assembly in this embodiment and includes an axially extending portion 20a having an end surface 340 abutting the end surface 38 of the sleeve 16 in a fashion identical tothat of the above embodiment. The axially ektending portion 20a and the circumferential exterior recess are similarly proportioned so that a space 40a exists between the end face 36 of the tube 12 and the end face 32a which corresponds to the end face of the tube 10 in the above embodiment.

The mating assemblies again provide for precise axial and radial alignment which may be visually inspected by the joint formed by the abutting end surfaces 340 and 38 on the outer periphery of the assembly. The space 40a is similarly provided to facilitate purging the weld area with a suitable gas. The mating assemblies, specifically the elbow 44, the tube 12, and the sleeve 16 are joined by'a single fusion weld bead 42a illustrated in the lower portion of FIG. 4. The weld bead 420 has a larger axial width at its inner extremities than the space 40a and a width at the outer surface of the mating assemblies at least equal to about twice the axial spacing between the space 400 and the abutting end surfaces 34a and 38, so that the mating assemblies are joined in a manner identical to that in the above embodiment. Although the embodiment illustrated in FIG. 4 provided the female assembly, it may have similarly provided the male assembly.

In many systems the tubing is subjected to vibration and/or torsional loads which tend to produce twisting and bending of the tube. Since the sleeves are anchored only at the weld interface such loading is not directly applied along the length of each of the sleeves and relative movement tends to occur betweenthe sleeves and the adjacent tubes surfaces with the amount of movement increasing with increased spacing from the weld. In many such instances, it is very desirable to provide a lubricating coating 49 (illustrated in FIG. 1) along the interengaging surfaces between each sleeve and the associated tube, at least along the interface at locations spaced from the weld. This is particularly desirable when the coupling is used to join materials such as titanium which tend to gall or fret under working conditions. Preferably, the interior portion of each sleeve, extending axially from the end surface remote from the tube end for a distance equal to about one-fourth'to one-half of the total sleeve length is provided with a dry lubricant coating 49.

Because the sleeve is subjected to relatively high temperatures during welding normal liquid film lubricants are not generally satisfactory. For this reason, it is preferable to use a dry lubricant film in which finely divided solid lubricant materials are dispersed in a bonding vehicle. Such vehicle is usually organic and serves to hold the lubricant material in place at least until the welding is completed. The binder may be of the type that drys such as by solvent evaporation with or without the application of heat, or may be of a type which is cured by a chemical reaction.

Under the thermal conditions occurring during welding, the binder may partially or completely decompose. However,

since a tight interengagement is provided along the interface in which the lubricant is located, it is not necessary in all in stances for the binder to maintain its binding function since such interengagement will retain the lubricant in place.

The solid lubricants may be of any known type such as M08 Sb ti or graphite or mixtures thereof. The resin binder may be any film forming material of a type known to those in the art. A satisfactory lubricating film has been obtained by surface treatment of the sleeve which employed a vapor blast with 220 grid aluminum oxide before applying the dry lubricant coating. A coating consisting of an epoxy bonded dry film lubricant containing M08 and Sb tl was then applied according to the process identified as Dow-Corning Process No. 1-3930." It was found that titanium couplings provided with such coating, when compared to similar couplings without the coating, were capable of absorbing far greater numbers of cycles of vibration and loading without failure.

Preferably, the coating is applied along both the inner and outer surfaces of each sleeve. When this is done the coating along the exterior surface provides a visual indication which may be used to properly orient the sleeve with respect to the tube during assembly. The coating may be applied to the tube end underlying the sleeve. However, in most cases such coating on the tube should terminate at a location spaced from the end of the tube so that the coating does not contaminate the weld.

in order to minimize the presence of stress concentration, it is also preferable to provide a generous radius 54 along the inner surface of each of the sleeves adjacent to their ends remote from the weld. This radius eliminates the sharply defined boundary line between the sleeves and the adjacent tube and thereby minimizes the presence of stress concentrations.

Although preferred embodiments of this invention are dis closed, it is to be understood that various modifications and rearrangements of parts may be resorted to without departing from the scope of the invention disclosed.

What is claimed is:

i. A coupling for use in forming a welded tube joint comprising a tube end assembly and a tubular mating part assembly, said tube end assembly including a tube extending to an end face and a sleeve positioned around said tube adjacent to said end face tightly engaging the outer surface of said tube, said sleeve havinga wall thickness which is substantially constant throughout a major portion of its axial extent and substantially less than the wall thickness of said tube, each of said assemblies providing an end face extending generally radially outward from the inner surface thereof, an end surface extending inwardly from the outermost surface of the assembly at a location axially spaced from the associated end face and a generally cylindrical surface extending between the associated end face and end surface, said cylindrical surface of one of said assemblies being an inner surface and said cylindrical surface of the other of said assemblies being an outer surface proportioned to telescope into and closely fit said cylindrical surface of said one assembly to laterally align said assemblies, said end surfaces mutually engaging when said assemblies are properly positioned for welding and providing an indication of axial alignment of said assemblies, all of said mating end surfaces of said assemblies being joined in a single weld bead formed by externally applied fusion heat, said weld bead having a width at the outer surface thereof at least equal to about twice the axial spacing between said and faces and said end surfaces and extending radially through said assemblies to join said end faces.

2. A coupling as set forth in claim 1 wherein the axial spac ing between said end face and end surface of said other assembly is less than the axial spacing between said end face and end surface of said one assembly, said end faces being spaced a predetermined amount when said end surfaces are in abutting engagement, said weld bead having a width at said inner surface at least equal to the spacing between said end faces.

3. A coupling as set forth in claim 1 wherein said assemblies are fonned of metal having a relatively low thermal conductivity and a relatively high notch sensitivity.

4. A coupling as set forth in claim ll wherein said tube is expanded within said sleeve to provide tight engagement therebetween, said sleeve being stressed in tension and said tube being stressed in compression.

5. A coupling as set forth in claim 4 wherein said one assembly is said tube end assembly and said sleeve projects beyond said end face of said tube, the projecting portion of said sleeve before assembly with said tube being flared outwardly toward said end surface, expansion of said tube within said sleeve causing the inner surface of said projecting portion of said sleeve to have a cylindrical shape with a radius substantially equal to the radius of the exterior surface of said tube.

6. A coupling as set forth in claim 1 wherein said tube end assembly is said other assembly, said cylindrical surface of said other assembly being provided by the outer surface of said tube adjacent to the end thereof.

7. A coupling as set forth in claim 1 wherein the inner surface of said sleeve is formed with an outwardly flaring portion of its end remote from said weld bead.

8. A coupling as set forth in claim ll wherein a lubricating film is provided along a substantial portion of the interface between said tube and sleeve extending inwardly from the end of said sleeve remote from said weld and terminating at a location spaced from said weld.

9. A coupling as set forth in claim 8 wherein said lubricating film is a dry lubricant coated on said sleeve and extending a distance equal to less than one-half of the length of said sleeve.

10. A coupling as set forth in claim 9 wherein said assemblies are formed of titanium or the like. 

1. A coupling for use in forming a welded tube joint comprising a tube end assembly and a tubular mating part assembly, said tube end assembly including a tube extending to an end face and a sleeve positioned around said tube adjacent to said end face tightly engaging the outer surface of said tube, said sleeve having a wall thickness which is substantially constant throughout a major portion of its axial extent and substantially less than the wall thickness of said tube, each of said assemblies providing an end face extending generally radially outward from the inner surface thereof, an end surface extending inwardly from the outermost surface of the assembly at a location axially spaced from the associated end face and a generally cylindrical surface extending between the associated end face and end surface, said cylindrical surface of one of said assemblies being an inner surface and said cylindrical surface of the other of said assemblies being an outer surface proportioned to telescope into and closely fit said cylindrical surface of said one assembly to laterally align said assemblies, said end surfaces mutually engaging when said assemblies are properly positioned for welding and providing an indication of axial alignment of said assemblies, all of said mating end surfaces of said assemblies being joined in a single weld bead formed by externally applied fusion heat, said weld bead having a width at the outer surface thereof at least equal to about twice the axial spacing between said end faces and said end surfaces and extending radially through said assemblies to join said end faces.
 2. A coupling as set forth in claim 1 wherein the axial spacing between said end face and end surface of said other assembly is less than the axial spacing between said end face and end surface of said one assembly, said end faces being spaced a predetermined amount when said end surfaces are in abutting engagement, said weld bead having a width at said inner surface at least equal to the spacing between said end faces.
 3. A coupling as set forth in claim 1 wherein said assemblies are formed of metal having a relatively low thermal conductivity and a relatively high notch sensitivity.
 4. A coupling as set forth in claim 1 wherein said tube is expanded within said sleeve to provide tight engagement therebetween, said sleeve being stressed in tension and said tube being stressed in compression.
 5. A coupling as set forth in claim 4 wherein said one assembly is said tube end assembly and said sleeve projects beyond said end face of said tube, the projecting portion of said sleeve before assembly with said tube being flared outwardly toward said end surface, expansion of said tube within said sleeve causing the inner surface of said projecting portion of said sleeve to have a cylindrical shape with a radius substantially equal to the radius of the exterior surface of said tube.
 6. A coupling as set forth in claim 1 wherein said tube end assembly is said other assembly, said cylindrical surface of said other assembly being provided by the outer surface of said tube adjacent to the end thereof.
 7. A coupling as seT forth in claim 1 wherein the inner surface of said sleeve is formed with an outwardly flaring portion of its end remote from said weld bead.
 8. A coupling as set forth in claim 1 wherein a lubricating film is provided along a substantial portion of the interface between said tube and sleeve extending inwardly from the end of said sleeve remote from said weld and terminating at a location spaced from said weld.
 9. A coupling as set forth in claim 8 wherein said lubricating film is a dry lubricant coated on said sleeve and extending a distance equal to less than one-half of the length of said sleeve.
 10. A coupling as set forth in claim 9 wherein said assemblies are formed of titanium or the like. 